Free Planet

From Astro Wars

New worlds available to be colonized are called Free Planets and are shown as such in your Star System Detail Screen. Free Planets have no owners until a Colony Ship arrives from a player with a high enough Culture level to take control of it. When colonized, the planet has no buildings and has a population level of 1.

Free Planets can also be used as 'jump points' to other planets, provided there are no Colony Ships in your fleet. Free planets can be held under siege.